1. Technical Field
The present invention relates to the structure and operation of electrode assemblies for electro-hydraulic forming processes.
2. Background
Electro-hydraulic forming (EHF) is a process in which a high voltage, stored charge is discharged across spaced electrodes that are disposed in a fluid filled chamber. An EHF system generally includes a chamber that is filled with fluid, for example water with a rust preventative. The electrodes are immersed in the fluid within the chamber. A sheet metal blank is placed on the chamber. A one-sided die is then placed on the blank. Air is then evacuated from both sides of the blank. The capacitor bank stores a charge and may provide between 5 to 50 kV through the electrodes.
The voltage applied to the electrodes creates a high temperature plasma channel. Current from the capacitors expands the plasma channel and fills the region surrounding the plasma channel with gas in the form of super heated steam which then transitions to a steam/water interface. Pressure builds within the chamber and results in a high intensity high velocity shock wave being formed in the liquid that is transmitted to the sheet metal blank. The sheet metal blank is driven into the die by the high velocity shock wave.
Traditional advantages over conventional sheet metal forming processes that are known include reduction in capital cost because only a one-sided die is required to form a panel. Recently, EHF processes have been proposed for forming sheet metal materials that are more difficult to form than low carbon steel. For example, the EHF process could be used to manufacture automotive and truck components from high strength steel, stainless steel or aluminum alloys. EHF processes are generally targeted at low volume stamping processes that may take advantage of the savings resulting from the use of a one-sided die.
The electrode assembly is subject to erosion caused by the shock wave and high temperature plasma. In addition, the fluid in the chamber tends to be corrosive. These conditions lead to erosion of both electrodes and insulation that fills the gap between the chamber and the electrodes. The shock wave resulting from discharge of the capacitors through the electrodes exerts a force on the electrode assembly tending to expel the electrode and insulation from the chamber. The electrode system must withstand the high pressure and high temperature plasma, as well as the corrosive water in the chamber. The electrodes must conduct energy into the chamber, maintain electrical isolation through the insulation, maintain the chamber in a water tight condition and constrain electrode motion during pressure pulses tending to eject the electrode from the chamber.
These and other problems are addressed in applicants' development as summarized below.